The basic operating mode of a DDD/AAI pacemaker is in the AAI mode—or more precisely a “pseudo-AAI” mode—with a single chamber atrial pacing (AAI mode stricto sensu), and a monitoring of ventricular activity. This operating mode is maintained as long as atrio-ventricular conduction is normal, that is, as long as each atrial event (either an atrial detection, corresponding to a spontaneous activity, or an atrial stimulation) is followed by an associated ventricular detection.
In certain circumstances, however, atrio-ventricular blocks (AVB) may appear, leading to a temporary disorder of the depolarization of the ventricle. In this case, as long as several conditions are met, the pacemaker automatically commutes to an automatic DDD mode, with parameters that are optimized for this situation involving a temporary AVB. After the disappearance of the AVB, and therefore after a re-establishment of atrio-ventricular conduction, the pacemaker automatically commutes back to AAI mode, as long as several other conditions of operation are met.
This principle of operation allows maintaining a spontaneous ventricular activity, for patients presenting an atrio-ventricular that is, most of time, normal.
Such a commutation between DDD and AAI operating modes is notably described in EP-A-0488904 and its counterpart U.S. Pat. No. 5,318,594 (commonly assigned herewith to ELA Medical), and EP-A-1346750 and its counterpart U.S. Published Patent application 2004/010292 (also commonly assigned to ELA Medical), which disclose the manner in which AVBs are detected and trigger the mode commutation and the AAISafeR mode operation, which disclosure is incorporated herein by reference in its entirety.
The present invention is based upon some observations made while actually following up patients, a short while after they were implanted with a device having the aforementioned “AAISafeR” feature (i.e. DDD/AAI device with automatic mode commutation).
Indeed, such devices are parameterized during their manufacturing process, either in automatic DDD mode (with no mode commutation), or in DDD/AAI with automatic mode commutation (i.e., with the “AAISafeR” feature activated). It is thus left to the practitioner to modify, if need be, the standard programming at the implantation, as a function of the patient's specific pathology.
However, for devices programmed with AAISafeR feature on, the absence of reprogramming by the practitioner may lead to side effects in certain patients for which such reprogramming would be necessary.
Indeed, before the implantation, the device only comprises the pulse generator, which is not yet equipped with adequate leads. The lead being not yet connected, the device will not detect any atrio-ventricular conduction (no ventricular signal is collected, as the lead is not yet connected). If the AAISafeR feature is on, that will induce a commutation to the DDD mode, which will be first temporary, then prolonged with a periodic test so as to allow a commutation back to AAI. This test is run after a relatively long delay after commutation towards DDD mode, so as to prevent commutations from AAI to DDD and then from DDD to AAI happening too quickly.
Thus, for those patients implanted in this manner, the AAISafeR mode allows a commutation back to AAI if the device detects a sustained ventricular activity, or after the periodic test that will be executed regularly, typically every morning.
Also, such a test, that is specific to the AAISafeR feature, makes sense only for patients having a permanent or quasi-permanent atrio-ventricular conduction.
On the other hand, for patients having a confirmed permanent atrio-ventricular block, such a test, which generates long ventricular cycles while tolerating the absence of ventricular activity over a limited period of time, is not appropriate. It can even be noxious, by creating in certain vulnerable patients some conditions favorable to the apparition of other disorders, which are very important to minimize, if not prevent.